A vehicle air conditioner is known to adjusts a temperature of a conditioned air in a manner that an evaporator disposed in an air conditioning duct cools air, and a heater core located downstream of the evaporator in a flow direction of the air heats the air flowing out of the evaporator. The vehicle air conditioner is configured to include a refrigeration cycle device, and Patent Literature etc. discloses such a vehicle air conditioner. The refrigeration cycle device of the vehicle air conditioner disclosed in Patent Literature 1 has a condenser, an evaporator, and a subcooling heat exchanger. In addition, the vehicle air conditioner has a bypass passage disposed in the air conditioning duct and introducing a cool air from the evaporator. The bypass passage is arranged parallel to a ventilation path extending to the heater core and to a cool air bypass passage. The subcooling heat exchanger is disposed in the bypass passage. The bypass passage is open when an air mix door opens the ventilation path extending to the heater core, and refrigerant, which is condensed in the condenser, is further cooled in the subcooling heat exchanger.